SU‐GG‐J‐48: Clinical Implementation of Varian On‐Board Imaging System

Abstract

Purpose: Two Varian on‐board imaging (OBI) systems have been installed and commissioned in our clinic. Over recent months, a daily QA procedure was developed to monitor system's performance and a clinical study was implemented to transition electronic portal image (EPI) guided to OBI guided prostate treatments. Method and Materials: A Penta‐Guide phantom (QUASAR™) is used for daily QA. The functions of match and couch auto motion in the OBI kilo‐voltage (kV) and OBI‐CBCT systems are tested. For the clinical study, to be finished in April, 2008, 14 prostate (78Gy/39) patients have been recruited. CBCT soft tissue‐based (ST) match and couch shift are performed twice a week and kV‐orthogonal fudical marker (FM) match and shift are executed 3 times a week for each patient before treatment. EPI FM match, our standard image guided procedure is used to verify the OBI match and couch motion. The differences are recorded. Results: Daily QA data over 5 months show that the coincidence between EPI and OBI after couch motion is 0.1±0.5mm, −0.2±0.6mm and −1.3±0.6mm (2σ) in RL, SI and AP direction, respectively. The AP mean was caused by the systematic couch motion error. For the clinical study, the preliminary data from the first 8 patients have been analyzed. The differences between OBI‐kV FM match and EPI FM match are −0.1±1.6mm, −0.4±1.8mm and −1.2±2.6mm (2σ) in RL, SI and AP direction, respectively. The differences between OBI‐CBCT ST match and EPI‐FM match are −0.9±4.1mm, −0.8±5.0mm and −1.6±5.1mm (2σ) in RL, SI and AP direction respectively. The AP mean is largely due to the systematic treatment couch motion error. Conclusion: The daily QA is comprehensive to capture systematic errors; OBI‐kV FM and EPI FM match agree within 3 mm in all three directions and CBCT‐ST match demonstrates larger variations of 5mm compared with EPI‐FM in three directions.